Microwave Water Heat

why you ask, cost

Not only would you need a magnetron that draws alot of current, you have to have a pump to circulate as its heating/running, not to mention on how you will get the water to pass through the micrwaves.

Again, just a thought, but if the regular water heaters rely on thermal flow, why wouldn't the microwave produce the same? Also, since the microwaves seem to penetrate glass, put the magnetron in a glass enclosure in the center of the tank. Are we down to only curing the cost? Everything once developed comes down in cost, so if it was mass produced maybe it would be worth it.....again, just a thought.

Magnetron's are mass produced, and it is a rather simple item, but I am not only talking about the cost of the equipment, I am talking about the energy use efficiencies.

p911

XXXXXXXXXX!!!!!!!!

Be very CAREFUL and CAUTIOUS with heating WATER with a MICROWAVE source.

This can even happen with a cup of water in a microwave oven:

The microwaves create "hyper heated pockets" in the water mass from which the water can explode into the atmosphere.

Stirring and/or "heat conductive" non metal material should be used to evacuate this energy.

The effect occurs more to boiling temperatures.

Many persons have been inflicted with severe burns in the face.

read and spread the word.

thats why it should be recirculating, you do not what flash sream issues. I just think its not a good application for microwaves

Allow me to read your answer with a lot of skepticism. Every time I heat my cup of soup in my 600 Watts microwave, I find myself saving a lot of energy in contrast to my electric stove of 2000 Watts, that takes 3 times the time to get my soup hot. With this practical knowledge, may I ask how to reverse calculate the power difference?

now heat your cup of coffee with opening the hot water tap (for insitant coffe).

When you list levels of efficiencies, its probally Hot water Heater, Micro Wave, Stove....not sure about the order of the last (2)

Now you have a small wattage Microwave at 600 watts, which on larger scales is nothing more than a fart in the wind.

And its not too hard to search the web for energy uses, between atleast the two Water Heater, Micro Wave, and get a comparizon of BTU's between the two. Which the BTU's requirement to raise the temperature of your coffee will be the same, but it is the energy consumed for the transfer of energy.

Do Not just look at the time it takes to heat your coffee look at the energy require to turn the electricity into micro wave, then to heat you coffee.

Skepticism is no substitute for intelligence. A range top transfers heat from burners to pot, and from pot to soup. Much of the heat misses the soup. With an immersion heater, as several other posters have stated, 100% of the heat transfers to the water, which in turn is well-insulated.

If you look at these new inductive range tops, where the range top induces eddy currents in a steel or iron pot, these work much faster than traditional burners, because the heat transfer to the pot is much more efficient. But still nothing like a totally immersed heating element.

emc_c

Why do you think electric immersion heaters have low efficiency? Practically all the electrical energy goes into the water, and you can't do much better than that. Losses from the hot water cylinder are down to the state of the lagging. Could avoid those losses with an instantaneous water heater. There are probably electric ones available, there are definitely gas-fired types.

Cheers...........Codey

I'll try again. Take a element, put it in the water, connect the power and what do you see? Hot Bubbles that just want to get "out" of the water and further ....the surrounding water having lots of difficulties to have contact with the element.

I don't blame the water, I wouldn't want to touch that hot element either?

One of the reasons the elements in their nice complete submerged water mass, burn down that easy.

That is because the elements are built to be replaced.

Here they even replace the whole boiler when that happens. There are different ones, with big surfaces, and lower watts/surface ratings - better controlled than the ice aged tank wall contact thermostats ....and.... more efficient. But they don't fit in that 1 1/4 to 1 1/2 inch hole.

The bubble are insulators, and you may get stratification in the temperature. But remember that you will also have incoming water, to breakup some of the laminar flows..........

Its not a perfect world though, is it?

Electric water heating elements are effectively 100% efficient. (In other words, there is no "waste heat" produced.) Essentially* all the heat produced by the element goes into the water, either directly or via the tank into which the element mounts. The slight inefficiency in a water heater is the insulation -- some of the heat of the water and tank leaks out into the environment. For this reason, point of use (instant) water heaters are more efficient in overall operation -- there is less time for the water to cool down.

A microwave heater would be less efficient, because the waste heat from the electronics would be more difficult to transfer into the water.

* There is minuscule leakage via thermal conductance of the wires supplying the heater element, etc.

I call 3-4 degrees temperature drop per hour not "slightly inefficient". Pardon me please.

Well, this appears to be not only feasible, but profitable.

These guys http://www.wanderport-ir.com/index.php?pg=products offer just such a tankless water heater, using microwave energy to heat the water. This spec sheet indicates 99% efficiency. Only 4-7 gallon a minute, though.

From the specs: "Electromagnetic penetration is infinite in a perfectly transparent substance and zero in reflective material (eg. metals). At the microwave frequency of 2.45 GHz, most energy is absorbed by water. Although it is also true that magnetrons are 70% effective, we have increased the way that these magnetrons can yet increase water temperature. An unwanted by-product produced by magnetrons in other conventional settings is heat, (almost 30%).

"We utilize this otherwise lost heat to cool the magnetrons and further heat the water through thermal transfer. Thus our efficiency rate improves substantially. Further, one might present the point in regards to the directionality of the microwave energy and the control of same."

I don't know... this sounds pretty good. I cannot find another manufacturer of this type of equipment. If this is really this good, why are these guys the only manufacturer to see the light?

I use an electric resistance water heater mounted as a shower head. Costs $30. Uses about 750 Watts. Instant on as soon as the water starts flowing, instant off as soon as the water stops flowing. Probably talking 4 to 7 gallons a minute total water flow when I have the temperature right. Hard to beat the economics of that...

Are you sure you don't mean 7500 watt? At 4 USgpm that gives ΔT about 7°C. 750 watt would be very economical, but not a very pleasant shower!

Cheers.........Codey

You are right- 7500. My computer was manufactured by the same outfit that did the Voyager computers, and aliens got in to it and shifted a memory bit, causing a loss of a 0. It is not at all possible that I mis-typed that!

Well, if you're going for a tankless heater, meaning hot water on demand, just-in-time, so to speak, then you need something besides a traditional immersion heater, because the immersion heater isn't making contact with enough water to give even heating on demand, only over a longer period of time over which the heating is integrated. It could be redesigned to do that, but here at least the microwave power source has the following benefit.

It makes sense to have a designed beam-width (i.e, antenna or radiating element) heating all the water passing through it (illuminated by it) evenly.

But again, the cost here is much higher than for a traditional tank. These heat-on-demand systems are much more expensive than the traditional technique, and they are sold on the claim that they don't waste energy by heating water that isn't needed, and that they have enough heating capacity to never run out of hot water.

emc_c

Eh? Electric tankless water heaters use immersion elements too...

Yes but it shows to be one of the worst efficient heat exchangers.

Quote:Electromagnetic penetration is infinite in a perfectly transparent substance. Unquote

Water is not transparent to microwaves (2.45 GHz). If it were to be, then the micro wave will just pass through without heating. The skin depth in water for this frequency is about 7cm. If the depth of water is more and the microwave comes in from the top, there will be no heating below this depth.

Bioramani

You are partially right:

In a microwave heating, the magnetron can be cooled by the same water you want to heat, then use the microwave generated to further heat the water. BUT the total efficiency is less than 100% because cooling the magnetron can never be back to ambiant temperature: thus some heat will still be lost there and can be substantial. the claim of 99% is not feasible and you will find that the way they work it out leaves a GAP??

An immersion heater produces the heat inside the water tank and thus all the generated heat will be there for the water. Any heat loss due to insulation or any other consideration will apply to the microwave system also...

Immersion heaters are nearly 100% efficient and generally not dangerous (and cheap and reliable).

Microwaves are not near 100% efficient and are dangerous (and expensive)

Smeaton.. Prey tell what you do with all the hot water you generated but did not use? Is it more efficient then to keep it hot ? So, let us say you used 50 liters from a 100 liter tank of HOT (your desired temp) the temperature of which falls as soon as you use a small percentage of it <15% and continues to fall exponentially as you use more. I have yet to hear of any domestic system of electric immersion heating that having heated the tank to the desired temperature is capable of delivering the same amount at the desired temperature on demand.

But if anyone knows of one, I am all ear's ( don't call me Dumbo)

Finally.. what portion of any latent heat in the emersion system is cost free at the point of delivery?

Smeaton is correct. The way to increase efficiency with electricity as an energy source is to use a heat pump-- one can expect from 3 to 6 times as much heat out as energy in with an air-to-water, ground-to-water, or water-to-water heat pump. Of the shelf technology.

The number of times you drop the soap in the shower is inversely proportional to the time remaining before your appointment.

It is very hard to increase the efficiency of an on-demand immersion heater mounted at the point of use where power is supplied only when water is flowing...

The most efficient water heater is a heat pump type.It is much cheaper to move heat than create it.

google it.